We investigated how cells in the visual system of the monkey are influenced by rapid eye movements. We found that in the visual cortical pathway of the monkey, stimuli before and after the rapid movement act to reduce the sensitivity of the system to that movement, but that the physiological mechanisms for the stimuli preceding and following the eye movement are quite different. Parallel experiments on perception of the same stimuli by human observers produced time courses of perceptual masking comparable to the effects seen at the single cell level in the monkey. In the other visual pathway, that to the superior colliculus, a visual masking effect has also been identified so that the masking effect is a general one in both visual pathways. The role of the superior colliculus in the initiation of eye movement was also investigated. The normal monkey makes many eye movements and the smaller ones of less than 15 degrees predominate. Following ablation of the colliculus, while monkeys were still able to detect visual stimuli in the central visual field and make eye movements to them, the monkeys made fewer spontaneous small saccades. In addition, they were no longer distracted by a visual stimulus in the visual field related to the damaged colliculus.